1. Field of the Invention
The present invention relates to a stepping motor for use in a rotary magnetic disc device and, in particular, to a stepping motor for a rotary magnetic disc device used as a magnetic recording/reproducing device in an electronic still camera or the like.
2. Description of the Prior Art
Recently, there has been developed an attractive electronic still camera system in which an image pickup device such as a solid image pickup element, an image pickup tube or the like is combined with a recording device employing as a recording medium thereof an expensive magnetic disc having a relatively larger storage capacity, such that an object can be still-photographed electronically and recorded into a rotating magnetic disc and the reproduction of the recorded image can be performed by means of a television system, a printer or the like which is provided separately from the electronic still camera system.
The magnetic disc that is used in such camera system is usually in the form of a magnetic disc pack. In the magnetic disc pack there is rotatably stored a magnetic disc which is capable of magnetic recording of still image information or the like, and such magnetic disc pack is used after it is mounted as a rotary magnetic disc device incorporated in an electronic camera.
There is generally well known a head carriage driver mechanism in the rotary magnetic disc device which is used to transmit a rotational force from a stepping motor to a head carriage through a gear reduction mechanism, a lead screw and the like, as a linear movement. In this drive system, a given number of pulses are applied from a control part to the stepping motor, so that a track-by-track feed can be performed.
By the way, in such a case as in the electronic still camera or the like where space is limited, it is necessary that all essential parts be compactly assembled within the rotary magnetic disc device.
However, a conventional stepping motor used in the rotatry magnetic disc device, as shown in FIG. 7, is composed of a solenoid coil 70, a yoke 72 enclosing the solenoid coil 70, a rotor magnet 74 which is loosely inserted into the coil 70, and a plurality of teeth 76 formed integrally with the yoke 72 and interposed between the coil 70 and the rotor magnet 74. In such structure, because the solenoid coil 70 is positioned in the outer periphery of the rotor magnet, the diameter of the coil 70 is large so that the stepping motor is also larger in size. Such large-size stepping motor provides an obstacle in assembling the electronic still camera and the like in a compact manner.